Most of the ice lost from the world's glaciers is lost through the calving of icebergs. An understanding of this process is vital to projections of sea-level rise, to reconstructing changes in the great ice sheets of the past, and to analyses of present and future changes in many Arctic glaciers. Unfortunately, the process is complex and no satisfactory calving relation that can be incorporated into numerical models has been developed and validated. A unique opportunity to do this is now at hand: An extensive data set on geometry, flow and calving of the rapidly disintegrating Columbia Glacier, Alaska, has been developed by the U.S. Geological Survey, and new developments in fracture mechanics now make it possible to compute crevasse interactions and other processes that are critical to the breakoff problem. The investigators will collect additional, highly-detailed strain and geometric data at and near the terminus of this glacier using primarily aerial photogrammetry. They will then use these and the existing data set in newly-developed fracture and flow models. These models, which use discrete displacement analysis (DDA) as well as finite element models, will be used to simulate breakoffs and define the interaction between calving and flow. The results will be tested to see if the current behavior of the glacier can be simulated well, and if so, to see if the 1978-95 history of change in this glacier can be modeled accurately. Then the generality of the modeling for other applications will be explored. It is expected that this study will produce 1) a detailed observational data set on dynamics and calving for use by others, 2) further insight into iceberg discharge mechanisms and the interrelations between calving and ice dynamics, 3) better knowledge of large-scale fracture processes in ice, 4) new glaciological modeling tools, such as DDA, and 5) an iceberg calving relation which will be useful for a wide range of paleoglaciological and current ice sheet and glacier investi gations as well as studies of the role of iceberg discharges in ice/ocean interactions.
